RANDOM INITIATION OF REPLICATION OF PLASMIDS P1 AND F (ORIS) WHEN INTEGRATED INTO THE ESCHERICHIA-COLI CHROMOSOME

We have constructed intP1 and intFs strains of Escherichia coli in whi ch the basic replicons of either plasmid P1 or plasmid F (oriS) were i ntegrated into an inactivated oriC, such that chromosome replication i s controlled by the integrated plasmid replicon. In this study, we hav e further analysed these strains, and density-shift experiments reveal ed that chromosome replication occurred randomly during the cell cycle . Flow-cytometry analyses of exponentially growing populations support ed this conclusion, and also showed that the DNA/mass ratio of the str ains decreased with increasing growth rate. Flow cytometry of exponent ially growing cultures treated with rifampicin demonstrated that initi ation of replication was uncoordinated in cells containing multiple re plication origins.